Microstructural and entropic engineering of Sn-based anodes for enhanced stress relaxation

다국어 초록 (Multilingual Abstract)

With the increasing demand for electric vehicles (EVs), portable devices, and energy storage systems (ESS), various anode candidates with high gravimetric and volumetric capacities are being explored for high-energy lithium-ion batteries (LIBs). As an alternative to graphite, other Ⅳ-group elements (Si, Ge, and Sn) have attracted great research interest owing to their ultrahigh theoretical gravimetric capacities. In particular, tin (Sn) has been considered the one of the next-generation alloy-based anode candidates due to its high gravimetric capacity (990mAh g-1, Li4.4Sn), low operating voltage (~0.6 V vs. Li/Li+), and high availability. However, Sn suffers from a significant volume expansion (~260%) during continuous redox reactions, resulting in particle pulverization, active material detachment, rapid capacity fading, and eventually, cell failure. This issue has made it difficult to hinder the commercialization of practical battery packs.
In 2000, composites based on alloying/conversion, alloying/alloying or conversion/conversion exhibited enhanced electrochemical performance, often outperforming their single-component counterparts fabricated at various scales, from micro-to atomic scale. Conceptually, one component undergoes lithiation while the other temporarily functions as an inactive buffering agent, and vice versa. These components alternately suppress the volume expansion, thereby providing enhanced electrode integrity. Research has been proposed to determine the exact mechanism of this volume buffering mechanism using in situ, ex situ, and other techniques. However, this mechanism has barely been established and understood.
This thesis introduces Sn-based composites by pairing tin with tin oxide, bismuth, zinc, and transition metals. Each element not only mitigates volume fluctuation but also effectively relieves the stress generated from lithiation throughout the particles, achieving improved cyclability and electrode integrity. Facile synthesis methods were utilized to develop composites with the optimal ratios, morphologies, and buffering effects (Sn@SnOx, SnBi, High entropy Zn2SnO4). Furthermore, the buffering effects in these pairings were thoroughly investigated via various in situ and ex situ analyses and simulations.
It is believed that these ideas and findings pave the way for designing the high-energy-density, alloy-based composites as anodes in lithium-ion and next-generation batteries.

목차 (Table of Contents)

• Chapter 1. INTRODUCTION 1
• 1.1. Research Motivation 1
• 1.2. Background and Principle of Lithium-ion Batteries 5
• 1.3. Tin-based anode: Advantages and Challenges 8
• 1.4. The State-of-the art Tin-based anodes 13
• 1.4.1. Alloying/insertion of Sn-based anodes 17
• 1.4.1. Alloying/conversion of Sn-based anodes 18
• 1.4.3. Alloying/alloying of Sn-based anodes 19
• 1.5. Objectives and scope of studies 21
• Chapter 2. ALLOYING/CONVERSION OF SN-BASED ANODE MATERIALS 26
• 2. Core-shell Sn@SnOx microparticles for stable Li-ion batteries 26
• 2.1. INTRODUCTION 26
• 2.2. Experimental methods 29
• 2.2.1. Materials 29
• 2.2.2. Synthesis of core-shell Sn@SnOx 29
• 2.2.3. Particle characterization 30
• 2.2.4. Electrochemical Characterization 32
• 2.3. Results and discussion 33
• 2.4. Conclusion 67
• Chapter 3. ALLOYING/ALLOYING OF SN-BASED ANODE MATERIALS 68
• 3. Microscale Tin Bismuth Alloy Prepared via Cooling Rate Control as Anode Material for High-Performance Lithium-Ion Batteries 68
• 3.1. INTRODUCTION 68
• 3.2. Experimental methods 74
• 3.2.1. Materials 74
• 3.2.2. Synthesis of SnBi Alloys 74
• 3.2.3. Particle characterization 75
• 3.2.4. Electrochemical characterization 76
• 3.2.5. Stress Evaluation 77
• 3.3. Results and discussion 78
• 3.3.1. Synthesis and Characterization 78
• 3.3.2. Li+ Storage Performance 96
• 3.3.3. Stress Evolution Analysis 111
• 3.3.4. Full-cell Test 118
• 3.4. Conclusion 121
• Chapter 4. CONVERSION/CONVERSION OF SN-BASED ANODE MATERIALS 123
• 4. High-entropy Zn2SnO4 inverse spinel structure as Anode Material for High-Performance Lithium-Ion Batteries 123
• 4.1. INTRODUCTION 123
• 4.2. Experimental methods 127
• 4.2.1 Materials 127
• 4.2.2. Synthesis of high entropy Zn2SnO4 composites 127
• 4.2.3. Particle characterization 128
• 4.2.4. Electrochemical measurements 129
• 4.3. Results and discussion 130
• 4.4. Conclusion 151
• Chapter 5. CONCLUSION 152
• References 156
• Appendix 181
• Appendix A. Supplementary Data for Chapter 2 181
• Appendix B. Supplementary Data for Chapter 3 194
• Appendix C. Supplementary Data for Chapter 4 228